The medical infusion pump art is one of great breadth and diversity. Even within the art of syringe pumps a great deal of work has been done.
Syringe pumps generally are used to infuse a relatively small quantity of concentrated medicament as opposed to large volume pumps which are designed to infuse accurately a medicament which is formed in admixture with a large quantity of diluent.
Syringe pumps run the gamut from highly accurate and correspondingly expensive electro mechanical pumps such as the Baxter AS40 and other devices from various manufacturers to very inexpensive and correspondingly less accurate disposables; an example thereof being the Disetronic Infusor, which is a galvanic cell, generating Hydrogen, attached to a syringe. Another example of a disposable infusion device is the SmartDoseII.TM. by River Medical Inc. This device uses an acid-base reaction to produce gas operative to collapse a bag of medicament.
As can be seen by a review of the disposable syringe pump art, of which the above are exemplary, disposable syringe pumps, particularly gas driven syringe pumps, lack the requisite accuracy to deliver many of the latest and most efficacious drugs, particularly drugs for oncology treatments and antibiotics and the like.
The instant invention provides for a level of accuracy similar to that of an electromechanical syringe pump whilst maintaining the simplicity and low cost associated with disposable devices. This accuracy is achieved by use of an accurately current-controlled electrochemical cell which preferentially transfers oxygen out of the air into a specially designed syringe having an essentially constant coefficient of friction throughout the length thereof against the syringe plunger.
An additional shortcoming of gas driven infusion devices is that as the drive gas is being generated there is a delay in infusion at the desired flow rate as the gas pressure rises. In the instant device, the syringe is prepressurized so as to minimize this lead time.
The electrochemistry of electrically driven cells is well characterized. The instant device preferentially uses a cell made of Nafion.RTM. from E.I. DuPont de Nemours & Co. Nafion is an acidic material which provides for the reaction: EQU 1/2O.sub.2 +2H.sup.+ +2e.sup.- .fwdarw.H.sub.2 O EQU H.sub.2 O.fwdarw.1/2O.sub.2 +2H.sup.+ +2e.sup.-
which serves to fill the syringe with oxygen gas. As can be seen from the above reaction, the water is not consumed but rather is recycled as the reaction continues. The water necessary for proton transport when the cell becomes excessively dehydrated is contained in the pump in a novel blotter arrangement which shall be subsequently described.
The combination of the novel electrochemical cell, blotter and prepressurized syringe as well as other aspects of the invention, which shall be subsequently described, provides for an accurate and cost effective pump.